In our Australian Patent Application No 10247/92, we have described a system for recycling concrete plant waste water. The system consists of a central. high pressure pump which draws in the polluted water through a series of devices, where atmospheric air is injected into it. The aerated water is then returned to the pit via jet nozzles located around the floor. The thrust produced by these nozzles rotates the water around the pit, the movement resulting in the encapsulation of the semi-hydrated cement particles in the air bubbles. By the principle of buoyancy, these particles expand and rise towards the surface, the rotating water naturally vectoring them towards the central pump. This allows for their recirculation through the system, or their diversion through the batching water system, and subsequent re-use in concrete production. Water from the agitator pit is also used to wash out truck agitator barrels, this cement rich water then being returned to the agitator pit via an aggregate and sand collector box.
The amount of cement present in the pit at any one time bears no relation to it's volume in weight, but depends on what is termed the "activity factor". For example, after a weekend of no plant production, the pit would have a very low activity ratio, that is more cement particles in relation to volume of water.
Accordingly, to maximise the benefits from the agitation system described above, a method of measuring the free cement content of a particular volume of waste water would be most beneficial.